What is the Linq.First equivalent in PowerShell?

Question

The snippet below detects from a list of files which of them is a Directory on Ftp

as C# it will be like below

var files = new List(){\"App         


        

Answer 1

Something like this...

$files = @("App_Data", "bin", "Content")
$line = "drwxr-xr-x 1 ftp ftp              0 Mar 18 22:41 App_Data"
$dir = $files | Where { $line.EndsWith($_) } | Select -First 1

These versions of the last line would all accomplish the same:

$dir = @($files | Where { $line.EndsWith($_) })[0]

$dir = $files | Where { $line.EndsWith($_) } | Select -index 0

$dir = $files | Where { $line.EndsWith($_) } | Select -First 1

It was pointed out that the above is not exactly equivalent in behavior to Linq.First because Linq.First throws exceptions in two cases:

• Throws ArgumentNullException when source or predicate is null.
• Throws InvalidOperationException when source sequence is empty or no element satisfies the condition in predicate.

If you wanted that behavior exactly, you'd need some extra guard code.

Answer 2

as Robert Groves said, Select-Object -First Occurence do the tricks, you can also use -Last Occurence.

by the way, like any other static .Net method you can use linq in powershell.

[Linq.Enumerable]::First($list)

[Linq.Enumerable]::Distinct($list)

[Linq.Enumerable]::Where($list, [Func[int,bool]]{ param($item) $item -gt 1 })

Answer 3

This is a really simple implementation for First:

function First($collection)
{
    foreach ($item in $collection)
    {
        return $item
    }
    return $null
}

Instead of returning $null, you could throw an InvalidOperationException exception.

Answer 4

Doug Finke produced a great video ( only 7 mins ) about converting C# to Powershell http://dougfinke.com/video/CSharpToPowerShell.html

Roberts example is very good indeed, though comma delimiting will implicitly be treated as an array

the shortest way of doing it would be to put it all into a single pipeline :

$dir = "App_Data", "bin", "Content" | % { if("drwxr-xr-x 1 ftp ftp              0 Mar 18 22:41 App_Data".EndsWith($_)) { $_ } } | select -first 1